25 August 2008

Some information on APIs removed in the Android 0.9 SDK beta

Earlier this week, we released a beta of the Android SDK. In the accompanying post, I mentioned that we had to remove some APIs from the platform for Android 1.0, and as a result they don't appear in the 0.9 beta SDK, and won't appear in 1.0-compatible SDKs. Today, I want to take a few minutes to explain why.

GTalkService

We were all really excited when the "XMPPService" (as it was called, at first) was included in the first early-look SDK. Once we brought in our security review team to examine Android, however, they soon realized that, as exciting as it is, the GTalkService has some fundamental security problems. Rich Cannings is one of our security researchers, and here's his explanation of the issues:

When I first read about GTalkService, I was both excited and scared. As a developer, I was interested in a feature that provided a simple interface to send messages between two Google Talk friends. The messages would appear on the receiving device as a standard Intent that was easy to handle. How simple and beautiful is that? Unfortunately, when I put my tin foil hat on, I recognized that things are a little more complicated than that.

We decided to postpone GTalkService's data-messaging functionality for the following reasons:

"Repurposing" Google Talk Friends

Google Talk friends are intended for a different purpose than that envisioned by the GTalkService. Your Google Talk friends can contact you at any time via IM. They can see your email address and often can see your real name. However, the idea of a Google Talk friend does not always line up with the types of people who may want to interact with via an Android application.

For example, imagine a really cool mobile Massively Multiplayer Online Roleplaying Game using GTalkService. You would have to add all the players to your Google Talk friends list in order to play with them. Next time you log in to Google Talk from your desktop or on the web, you would notice that you have many new "friends". You may not want to chat with these friends -- and perhaps worse, you may not want them to know what your real name or email is.

We do realize that Android users will want to interact with other Android users anonymously and for short periods of time, especially in gaming scenarios. Unfortunately, it turns out that using Instant Messaging is not really a good way to do that.

Verifying Remote Intent Senders

Intents were designed to send messages within the device. The Intent subsystem can conclusively determine who sent Intents only when the Intents originate from the same device that services the Intent. When Intents come from other devices, the Intent subsystem cannot determine what application sent the Intent.

This can lead to a variety of problems. At first, remote applications could send arbitrary Intents, meaning that your Google Talk friends had almost the same control of your device as you did. Even once that issue was resolved, we recognized that we could not trust the identity of the application who sent the request. We could only trust the identity of the user. So a "bad" application on your friend's device could send a message to a "good" application on your device which would negatively affect the good application.

In the end, we determined that the Intent system, as designed for local use, did not lend itself well to being the vehicle for a Remote Procedure Call (RPC).

Placing Too Much Security Burden on Developers

As originally designed, the GTalkService placed a significant burden on the application developer to avoid security flaws and perform user and relationship management. An Android application using GTalkService would be reachable from all of the user's Google Talk friends, and a flaw in that application could pose an inviting target to a malicious "friend" or automated malware. There are automated mechanisms that could be used to help protect vulnerable applications or stop the spread of malware, but the deployment of these technologies was not possible in time for the launch of the first Android handsets.

Although we would have loved to ship this service, in the end, the Android team decided to pull the API instead of exposing users to risk and breaking compatibility with a future, more secure version of the feature. We think it's obvious that this kind of functionality would be incredibly useful, and would open lots of new doors for developers. One of our top priorities after the first devices ship is to develop a device-to-device (and possibly device-to-server) RPC mechanism that is fast, reliable, and protective of developers and users alike.

As a final note, I want to point out that since the GTalkService was always a Google "value-added" service anyway, it was never guaranteed that it would be present on every Android device. That is, GTalkService was never part of core Android. As a result this change actually allows us the potential to build a new system that is part of the core of a future version of Android.

Bluetooth API

The 1.0 version of Android and the first devices will include support for Bluetooth; for instance, Android will support Bluetooth headsets. In the early-look SDKs, there was an incomplete draft of an API that exposed Bluetooth functionality to developers. Unfortunately we had to remove that API from the 1.0 release. To get the skinny on why, I contacted Nick Pelly, one of the Android engineers responsible for that functionality. Here's the story on Bluetooth, in Nick's words:

The reason is that we plain ran out of time. The Android Bluetooth API was pretty far along, but needs some clean-up before we can commit to it for the SDK. Keep in mind that putting it in the 1.0 SDK would have locked us into that API for years to come.

Here's an example of the problems in the API. Client code is required to pass around IBluetoothDeviceCallback objects in order to receive asynchronous callbacks, but IBluetoothDeviceCallback is meant to be an internal interface. That client code would break the moment we added new callbacks to IBluetoothDeviceCallback.aidl. This is not a recipe for future-proof apps.

To make things even more tricky, the recent introduction of the bluez 4.x series brings its own new API. The Android Bluetooth stack uses bluez for GAP and SDP so you'll see more than a passing resemblance to bluez's interfaces in Android. The bluez 4.x change requires us to carefully consider how to structure our API for the future. Again, remember that once we settle on an interface we need to support it for years going forward.

Rather than ship a broken API that we knew was going to change a lot, we chose not to include it. We absolutely intend to support a Bluetooth API in a future release, although we don't know exactly when that will be. This should include some tasty features, such as:

Bindings to GAP and SDP functionality.

Access to RFCOMM and SCO sockets.

Potentially, L2CAP socket support from Java. (This one is under consideration.)

An API to our headset and handsfree profiles.

On a personal note, Nick adds, "I would love nothing more than to start seeing some neat third-party applications and games over Bluetooth. In my opinion, Bluetooth is completely under-utilized on most mobile platforms and I'm excited to someday see what the developer community can do with Android."

I'm definitely bummed about these API removals. I was particularly looking forward to the P2P capabilities offered by GTalkService, but, as always, user security and privacy must come first. In all these cases, we'll work with the developer community to create some great APIs that balance these concerns.